//1.
            this.Invoke(new ThreadStart(delegate
            {
                textBox1.AppendText(" + "\r\n");
            }));
            //2.
            this.Invoke(new MethodInvoker(delegate
            {
                textBox1.AppendText(" + "\r\n");
            }));
            //3.
            this.Invoke(new Action(
            () => { textBox1.AppendText(" + "\r\n"); }));
            //4.
            this.Invoke(new EventHandler(delegate
            {
                 textBox1.AppendText(" + "\r\n");
            }));